When is it necessary to use a refrigerant reclaiming machine?

A refrigerant reclaiming machine is essential for safely recovering refrigerants during servicing of a refrigeration system. This practice is critical for adhering to environmental regulations and ensuring the safety of the technician. When a refrigeration system is serviced, especially during repair or maintenance activities, there is a need to collect and contain the refrigerant to prevent its release into the atmosphere, which can be harmful and is often illegal under various environmental protection laws.

Using a reclaiming machine allows for the proper recovery, recycling, or disposal of refrigerants, ensuring that they do not contribute to ozone depletion or global warming. It's a crucial step to protect both the environment and human health. This procedure is specifically required when the system is not functioning correctly or needs to be opened for inspection or repair, making it a standard practice in the industry.

In contrast, recovering refrigerants is not necessary or appropriate during an initial system installation, when the system is operating normally, or in scenarios where the system is empty and no refrigerants remain. Therefore, the focus on servicing and safely recovering refrigerants in option D highlights the importance of responsible refrigerant management practices.